use anyhow::Result;
use serde::{Deserialize, Serialize};
use std::time::{Duration, Instant};
use tracing::info;

/// Query processor for executing database queries
#[derive(Debug)]
pub struct QueryProcessor {
    query_history: Vec<QueryExecution>,
    max_history: usize,
}

/// Query execution result
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QueryResult {
    pub query: String,
    pub rows_affected: Option<u64>,
    pub execution_time: Duration,
    pub columns: Vec<ColumnInfo>,
    pub rows: Vec<Vec<serde_json::Value>>,
    pub error: Option<String>,
}

/// Query execution record
#[derive(Debug, Clone)]
pub struct QueryExecution {
    pub query: String,
    pub result: QueryResult,
    pub timestamp: Instant,
}

/// Column information
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ColumnInfo {
    pub name: String,
    pub data_type: String,
    pub nullable: bool,
    pub primary_key: bool,
}

impl QueryProcessor {
    /// Create a new query processor
    pub fn new() -> Self {
        Self {
            query_history: Vec::new(),
            max_history: 1000,
        }
    }
    
    /// Execute a SQL query
    pub async fn execute_query(&mut self, query: &str) -> Result<QueryResult> {
        info!("Executing query: {}", query);
        let start_time = Instant::now();

        // For now, this is a placeholder implementation
        // In a real implementation, this would use the database connection
        let execution_time = start_time.elapsed();

        // Parse query type to provide appropriate mock response
        let query_lower = query.trim().to_lowercase();
        let (rows_affected, columns, rows) = if query_lower.starts_with("select") {
            // Mock SELECT result
            let columns = vec![
                ColumnInfo {
                    name: "id".to_string(),
                    data_type: "INTEGER".to_string(),
                    nullable: false,
                    primary_key: true,
                },
                ColumnInfo {
                    name: "name".to_string(),
                    data_type: "VARCHAR".to_string(),
                    nullable: true,
                    primary_key: false,
                },
            ];

            let rows = vec![
                vec![
                    serde_json::Value::Number(serde_json::Number::from(1)),
                    serde_json::Value::String("John Doe".to_string()),
                ],
                vec![
                    serde_json::Value::Number(serde_json::Number::from(2)),
                    serde_json::Value::String("Jane Smith".to_string()),
                ],
            ];

            (None, columns, rows)
        } else if query_lower.starts_with("insert") ||
                  query_lower.starts_with("update") ||
                  query_lower.starts_with("delete") {
            // Mock DML result
            (Some(1), vec![], vec![])
        } else {
            // Mock DDL or other result
            (Some(0), vec![], vec![])
        };

        let result = QueryResult {
            query: query.to_string(),
            rows_affected,
            execution_time,
            columns,
            rows,
            error: None,
        };

        // Add to history
        self.add_to_history(QueryExecution {
            query: query.to_string(),
            result: result.clone(),
            timestamp: start_time,
        });

        Ok(result)
    }
    
    /// Validate SQL syntax
    pub fn validate_sql(&self, query: &str) -> Result<bool> {
        info!("Validating SQL: {}", query);
        
        // TODO: Implement SQL validation
        // This is a placeholder implementation
        
        if query.trim().is_empty() {
            return Ok(false);
        }
        
        Ok(true)
    }
    
    /// Format SQL query
    pub fn format_sql(&self, query: &str) -> Result<String> {
        info!("Formatting SQL query");
        
        // TODO: Implement SQL formatting
        // This is a placeholder implementation
        
        Ok(query.to_string())
    }
    
    /// Get query history
    pub fn get_history(&self) -> &[QueryExecution] {
        &self.query_history
    }
    
    /// Clear query history
    pub fn clear_history(&mut self) {
        self.query_history.clear();
    }
    
    /// Add query execution to history
    fn add_to_history(&mut self, execution: QueryExecution) {
        self.query_history.push(execution);
        
        // Limit history size
        if self.query_history.len() > self.max_history {
            self.query_history.remove(0);
        }
    }
    
    /// Get query statistics
    pub fn get_statistics(&self) -> QueryStatistics {
        let total_queries = self.query_history.len();
        let successful_queries = self.query_history.iter()
            .filter(|exec| exec.result.error.is_none())
            .count();
        
        let average_execution_time = if total_queries > 0 {
            let total_time: Duration = self.query_history.iter()
                .map(|exec| exec.result.execution_time)
                .sum();
            total_time / total_queries as u32
        } else {
            Duration::from_secs(0)
        };
        
        QueryStatistics {
            total_queries,
            successful_queries,
            failed_queries: total_queries - successful_queries,
            average_execution_time,
        }
    }
}

/// Query execution statistics
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QueryStatistics {
    pub total_queries: usize,
    pub successful_queries: usize,
    pub failed_queries: usize,
    pub average_execution_time: Duration,
}

impl Default for QueryProcessor {
    fn default() -> Self {
        Self::new()
    }
}
